DROPSTONE PETROLOGY, COMPOSITIONAL VARIATION, AND PROJECTED TERRESTRIAL PROVENANCE, WEDDELL SEA, ANTARCTICA

Antarctic bedrock is obscured by ice. Plate tectonic reconstructions, nunataks and geophysics provide information about the underlying geology. Dropstones and sediments recovered in circum-Antarctic cores and dredge hauls also provide critical information. The ability of the East Antarctic Ice Sheet (EAIS), to entrain clasts from bedrock and transport material offshore provides terrigenous evidence of bedrock composition. Today, the East Antarctic Ice Sheet, drains Coats and Dronning Maud Land into the Weddell Sea. According to Deconto and Pollard’s modeling (2009), this area of Antarctica has had a steady ice-sheet presence since continental glaciation began.

Our investigation examines dropstones from ODP (Ocean Drilling Program) Sites 691, 692, and 693, collected in 1987 from the margins of Wegener Canyon. Sites 691 and 692 had poor sediment recovery complicated by pebble and cobble deposits. These dropstones are not in stratigraphic context and are more like those recovered in dredge hauls. In contrast some dropstones from Site 693 sediment cores are considered in place.

The three analyses were performed on each dropstone (1) petrographic descriptions for mineralogy, texture, and modal variance; (2) Scanning Electron Microscopy (SEM) for mineralogical compositions, texture, and empirical variance; and (3) X-Ray Fluorescence (XRF) for major and trace elemental compositions; and (4) testing the viability of using handheld XRF Bruker Tracer IV to recover elemental data from small dropstones (>1.5g). These analyses show a much wider range of source areas than would be anticipated from the known bedrock geology.